Spark ignition apparatus for internal combustion engine



July 7, 1964 M. H. SPARK IGNITION ROBERTS E'I'AL APPARATUS FOR INTERNALCOMBUSTION ENGINE Filed Feb. 6. 1961 United States Patent 3,140,423SPARK IGNITION APPARATUS FOR INTERVAL COMBUSTION ENGINE Maldwyn HughRoberts, Sutton Coldfield, David Warwick Lloyd Clamp, Birmingham, andNorman Alfred Jukes, Walsall, England, assignors to Joseph Lucas(Industries) Limited, Birmingham, England Filed Feb. 6, 1961, Ser. No.87,182 1 Claim. (Cl. 315-401) This invention relates to spark ignitionapparatus for internal combustion engines, and of the kind including anignition coil.

Ordinarily, the coil comprises a primary and a secondary winding mountedon an iron core, and current is supplied to the primary winding from astorage battery through a rotary interrupter driven by the engine. Oneof the factors which adversely afiects the efficiency of an ignitioncoil of conventional construction is associated with sparking at theinterrupter contacts and the amount of electromagnetic energy which canbe transmitted through the coil is limited by the amount of currentwhich can be eifectively controlled by the interrupter.

The primary object of the present invention is to provide an ignitioncoil in a form whereby the above disadvantage can be minimised orobviated.

An ignition coil in accordance with the invention comprises a primarywinding, a secondary winding, a pilot winding, and a control winding allmounted on an iron core, the function of the pilot winding being toeffect excitation of the control Winding by an intermittent currentsupplied under the control of an interrupter, and the function of thecontrol winding being to control a transistor through which energisingcurrent is supplied to the primary winding.

The invention further resides in an ignition system comprising a coil asspecified in the preceding paragraph, an interrupter for controlling thesupply of current from a battery to the primary winding, a transistorfor controlling the supply of current from the battery to the primarywinding, and a diode interconnecting the ends of the primary winding.

An example of the invention is illustrated diagrammatically in theaccompanying drawing.

Referring to the drawing there is provided an ignition coil comprisingan iron core 1 on which is mounted a primary winding 2 capable ofgenerating the required magneto flux in the core 1 by a current suppliedfrom a source of direct or rectified alternating current such as, forexample, a 12-volt battery. Also on the core are mounted a secondarywinding 3 adapted to produce the required sparking voltage andconnectible to the engine spark plugs 15 in turn through a distributor14, a pilot winding 4 and a control winding 5.

There is further provided a pair of terminals 6, 7 adapted forconnection to the battery so as to be of negative and positive polarityin use respectively. One end of the winding 4 is connected to theterminal 6 through a capacitor 8 and a resistor 9, whilst the other endof the winding 4 is connected to the terminal 7 and through anengine-driven interrupter to a point intermediate the capacitor 8 andresistor 9. Further, one end of the winding 2 is connected to theterminal 6, whilst its other end is connected to the terminal 7 throughthe collector and emitter terminals of a p-n-p type transistor 11, thebase terminal of which is connected to the terminal 7 through thewinding 5. Moreover, the ends of the winding 2 are bridged by a diode12.

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In operation, whilst the interrupter 10 is open the capacitor 8 ischarged. On closing of the interrupter 10, however, the capacitordischarges through the winding 4. The resulting partial magnetisation ofthe core 1 includes a voltage in the winding 5, which initiates theaction of the transistor 1. Current is passed through the transistor tothe winding 2, increasing rapidly by regenerative action and therebycausing rapid magnetisation of the core, and inducing a high voltage inthe winding 3. The primary current reaches its peak value (at which thecore is magnetically saturated) in a very short period; when this valueis reached, there is no further change of flux in the core, and nofurther energy fed back to the winding 5. The transistor thus reverts toits initial state and interrupts the current in the primary circuit. Theback induced in the winding 2 by the switching off of the transistor isconducted through the diode 12, which suppresses high voltage peakswhich would otherwise damage the transistor.

If desired, either of the terminals 6, 7 could be earthed, butpreferably the terminal 7 is earthed so as to obviate the need forinsulating both contacts of the interrupter 10. Further, with suitablemodifications an n-p-ntransistor could be employed.

Since the current required in the pilot circuit is small, no seriousresult can follow from any small amount of sparking that may occur atthe interrupter contacts. Con sequently, a greater uniformity of actionoccurs in the secondary winding, both as regards the timing of thedischarge and the energy content of the sparks at the sparking plugs ofengine. The arrangement illustrated has the additional advantage thatthe danger of large currents being drawn through the pilot winding inthe event of the engine becoming stalled with the interrupter closed isobviated.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:

Spark ignition apparatus for an internal combustion engine, comprising adirect current source, an ignition transformer having a core, a primarywinding on the core connected to the direct current source, and asecondary winding on the core connectible through a distributor to sparkplugs of the engine in turn, a monostable oscillator operation of whichcauses rising current to flow in the primary winding to induce a sparkat one of said plugs, said oscillator including a transistor in serieswith the primary winding, a control winding on the core connecting thebase and emitter of the transistor for providing feedback thereto, apilot winding on the core for inducing a voltage in the control winding,one end of the pilot winding being connected to one terminal of thedirect current source, and a capacitor and resistor connected in seriesbetween the other end of the pilot winding and the other terminal of thedirect current source, the apparatus further including an interrupterdriven by the engine and connected across the pilot winding andcapacitor for operating the oscillator, upon closing of the interrupter,in timed relationship to the engine, and a diode connected across theprimary winding for absorbing back electromotive force induced thereinafter the production of each spark.

References Cited in the file of this patent UNITED STATES PATENTS2,878,298 Giacoletto Mar. 17, 1959 3,007,082 Kappele Oct. 31, 19613,016,477 Naborowski Jan. 9, 1962

